Weed and grass trimmers have been developed which employ a rotatable hub with a short length of flexible nylon or other plastic line extending from the hub. When the hub is rotated (typically, at speeds from 6,000 RPM to 12,000 RPM), the tip of the line extending from the hub provides the cutting or trimmer action. Grass and weed trimmers using this principle of operation have become popular for their versatility of use and because the flexible trim line is safer to use that rigid rotating steel blades.
Various types of devices have been developed using such trim lines. Typically, rotating line trimmers or rotating string trimmers employ a trimmer line which generally has a circular cross section. The line, in many trimmers, is wound on a storage reel in the hub of the device, and is fed out of a hole or a plurality of holes in the hub in discrete amounts, as the end breaks off or wears off. Trimmers of this type sometimes are referred to as “bump and feed” trimmers. If the line breaks off, the bottom of the storage reel is bumped while the hub continues rotating to cause a spring release of the line within the trimmer. A short length of line then plays out through a hole in the hub by means of centrifugal force. Typically, the smaller (2½″ diameter to 3½″ diameter) head bump and feed string trimmers use relatively small diameter line, normally in the range of 0.65″ to 0.080″ diameter, since the smaller diameter flexible line functions better for the centrifugal feeding of such smaller diameter bump and feed heads.
A problem exists with all bump and feed trimmers, however, in that frequently the line which is wound on the storage reel in the hub tends to become stuck, either due to partial fusion of the line in the hub caused by high frequency vibration, or by successive turns of the line wound on the hub becoming somewhat entangled. As a result, feeding of the line from the hub when desired does not always take place. When this occurs, it is necessary to remove the hub from the string trimmer device and manually extract the desired length of line prior to re-attaching the hub of the device. This is a time consuming and frustrating experience for many users of flexible line string trimmers. It is particularly frustrating for commercial landscapers because of the amount of lost time required to remove the hub, extract the line, and then re-attach the hub before operation can resume.
Efforts to overcome the inherent disadvantages of bump and feed trimmers have included the development of heads designed to accept fixed lengths of line, which are inserted into the head and held in place by various techniques. Once such device is disclosed in the patent to U.S. Pat. No. 5,615,543 Caffey. This patent employs a cut length of line having an enlarged portion or flange at one end. A small entry hole is located in the periphery of the head adjacent a larger exit hole. The line is inserted from outside the periphery of the head into the insert hole, where the enlarged end or flange on the line meets an abutment and is held in place. The line then is grasped from the hollow interior of the head and pushed through the exit hole and pulled tight. The bottom of the head is open to allow this access to both the interior and exterior of the head. A disadvantage of this device is the requirement for the operator to insert the line from outside the periphery of the head, then turn the head over, and reinsert the line back through the exit hole each time a line is to be inserted into the machine. Removal of a line is the reverse of the order mentioned. It is necessary to have access to the head both from the exterior periphery and from the bottom in order to accomplish insertion and removal of line segments. Multiple line segments (two are shown in the patent) may be inserted on opposite sides of the head.
The U.S. Pat. No. 5,023,998 to Masciarella is another attempt at the design of a string trimmer cutting machine utilizing fixed lengths of line. In the Masciarella patent, line segments are inserted into the machine from the open bottom by manipulating the line around guide wedges in a generally serpentine path on opposite sides of the head. Two line segments, each extending diametrically across the head and crossing at 90° angles, may be used to allow the head to have four lengths or ends of line extending from it. When a new length of line needs to be inserted, the old line must be removed; and this requires manipulating the line past the wedges once again in order to permit the line to be taken out of the machine. A new line then must be guided into place around the wedges or guide surfaces. Because the guide surfaces are close together, it becomes difficult to install, and particularly to remove, sections of nylon line from a trimmer head having the design shown in the '998 patent. This difficulty results in excessive time being consumed for the removal and replacement of line segments.
The U.S. Pat. No. 6,035,618 to Fogle also is directed to a fixed line trimmer head using a single length of line extending from diametrically opposite sides of the trimmer head. The trimmer head of the Fogle '618 patent overcomes the disadvantages of the devices discussed above. The trimmer head of Fogle employs a pattern of pairs of entry and exit holes for inserting a fixed length of trimmer line through a pair of relatively closely spaced entry holes, and then extending each end of the line out through exit holes located in the head. The entry holes and exit holes are offset from one another in different planes perpendicular to the axis of the trimmer head, and securely hold the line in place during use of the trimmer. It is relatively easy to remove an expended section of line and replace it with a new section of line when necessary. The fixed line trimmer head of the Fogle '618 patent, however, does require the user to manually insert the opposite ends of the line through the two entry holes, and then again manually to insert each of the ends of the line segment into the exit holes in the head whenever line replacement is required. This is indicated somewhat in FIG. 9 of the Fogle patent. Because of the necessity to manually insert the ends of a line segment through separate entry and exit holes for each length of the line, the user is required to have access through the bottom of the hollow trimmer head in order to extend the ends of the line into the exit holes for use.
The U.S. Pat. No. 6,457,242 to Fogle eliminates the necessity for access to the interior of the head through the bottom while employing a single fixed length of trimmer line. In the Fogle '242 patent, a pair of entry holes are located on the exterior surface of the head in a similar manner to the position for the entry holes disclosed in the Fogle '618 patent. In the Fogle '242 patent, however, the two ends of the line inserted into the adjacent entry holes are internally guided through arcuate guide channels formed in an insert in the interior of the head to exit out of the line exit holes. Once the line has exited from the diametrically opposed exit holes, it is pulled tightly and the offset position axially of the entry holes with the exit holes, combined with the arcuate guide paths, firmly holds the line in place during use. Removal of the line is readily effected by grasping it from outside the housing at the loop between the two entry holes and pulling it out in the reverse direction from insertion. Consequently, removal and replacement of a line is greatly facilitated through the use of the Fogle '242 head. The Fogle '242 patent also discloses the use of two different sizes of entry holes located on opposite sides of the head to accommodate lines of smaller diameters on one side and lines of larger diameters on the other side. If a change from lines of one diameter set to a different diameter set is required, the arcuate guide insert is rotated 180° to accommodate the entry holes on the opposite side of the head. This requires removal and replacement of the insert carrying the guide channels whenever a change from one range of line sizes to a different range of sizes is desired.
It is desirable to provide a fixed length line trimmer head with greater versatility and ease of operation which overcomes the disadvantages of the prior art devices.